What Do You Think Of This?
- Thread starter johnr9q@yahoo.com
- Start date
Joe K
Well-known member
Neither nut look to be original.
The rods are made with integral studs: i.e. the distance from the cotter pin hole to the shoulder of the rod is the same on both sides. And you can't change it.
The usual cotter nuts would have room to line up the slots and place a cotter. Your left in the pix MAY be original. But seems a bit "thin."
The right nut in the pix definitely something out of a coffee can somewhere.
When my engine was rebuilt the rebuilder used "nyloc" style nuts - no cotter pin. I don't think the left nut is one of those as you usually see a ring of "plastic" surrounding the stud.
"You'll thank me for these later" he said.
And yes Richard (Knight) I have.
Dippers point to the camshaft side.
Joe K
The rods are made with integral studs: i.e. the distance from the cotter pin hole to the shoulder of the rod is the same on both sides. And you can't change it.
The usual cotter nuts would have room to line up the slots and place a cotter. Your left in the pix MAY be original. But seems a bit "thin."
The right nut in the pix definitely something out of a coffee can somewhere.
When my engine was rebuilt the rebuilder used "nyloc" style nuts - no cotter pin. I don't think the left nut is one of those as you usually see a ring of "plastic" surrounding the stud.
"You'll thank me for these later" he said.
And yes Richard (Knight) I have.
Dippers point to the camshaft side.
Joe K
Last edited:
Personally, I would remove the tall nut and replace it with a shorter one and use a cotter pin. Don't forget to check the tension with a torque wrench. After that, remove the cotter pins and check ALL the rod caps with a torque wrench for proper tension and replace the cotter pins. You're already in there, why chance it?
After looking at your photo again, I noticed something else that would be a good idea to correct; after checking all the rod cap nuts for proper torque, install all new cotter pins and be sure to carefully fold them flat against the sides of the nut. I recently dismantled an engine that the previous owner failed to do that and some of the pins had half of the pin broken off and were laying in the dipper tray. I assume since they weren't correctly installed that centrifugal force had fatigued and weakened them enough to fail. Might save you some grief down the road. One of the pins in your photo shows what I'm talking about.
Joe K
Well-known member
I think I've told my story of driving the Mid-Cape Highway on a busy holiday(vacation) period - being in a line of traffic going 45mph and having the engine suddenly sound like it is self destructing.
You gotta understand that engine was about 0.003 egg-shaped on all the rod bearings. When assembled it made a "whuppa-whuppa" while idling. Self destructing it made a "Banga-Banga" sound.
I had assembled it in the theory of "shave the caps" until it started to bind on the eggs, and then drove it on the edge of seizing. The vibration apparently was enough to "wiggle" the caps, wear the cotter pin until it fell into the oil pan. The nut was soon after.
And with one nut I was lucky I didn't throw a rod through the side of the block. Keeping the car down to about 20mph I was able to "limp" (literally) home.
It was at that time I retired the engine and switched over to the freshly rebuilt Knight engine.
Joe K
You gotta understand that engine was about 0.003 egg-shaped on all the rod bearings. When assembled it made a "whuppa-whuppa" while idling. Self destructing it made a "Banga-Banga" sound.
I had assembled it in the theory of "shave the caps" until it started to bind on the eggs, and then drove it on the edge of seizing. The vibration apparently was enough to "wiggle" the caps, wear the cotter pin until it fell into the oil pan. The nut was soon after.
And with one nut I was lucky I didn't throw a rod through the side of the block. Keeping the car down to about 20mph I was able to "limp" (literally) home.
It was at that time I retired the engine and switched over to the freshly rebuilt Knight engine.
Joe K
mercman from oz
Well-known member
This is the rod bearing. One of the nuts has a cotterpin the other nut doesn't have a cotterpin but is taller. None of the rod bearings are like this. What Gives?
johnr9q@yahoo.com
Senior Member
mcgarrett, with the head of the cotterpin into the slot on the bolt, it looks like the pins naturally want to be bent in the way they are in the picture
johnr9q@yahoo.com
Senior Member
mcgarrett, I see what yiu are saying. The one you are looking at is in the middle of removal
Joe K
Well-known member
In the 1980s Richard Knight was rebuilding Model A engines in Magnolia, MA (out on the Gloucester Point) I think I have his town name correct. (Kettle Cove?)
Richard is still around, no longer doing engines (you gotta quit some time) but contributes on this forum occasionally.
Of the engine that got taken out, it has been joined by about four other engines of "donation" - and all about the same degree of "worn-out."
As to a tow - below about 30mph, the truck did fine - but it could have ended much worse. I was most concerned with the traffic on the Mid-Cape. But by then I knew most of the back-roads and switch-offs - and could return via the "Service Road."
OBTW, the loose nut and the pieces of the cotter pin were found in the bottom of the oil pan. But this is logical.
Joe K
Last edited:
OK, sounds like you know what you're doing. I hope this repair gets you back on the road soon.
Klattu1929
Senior Member
If cotter pins had a problem with problem with failure, then they would not be so widely used in the aircraft industry. What kind of temperature does it take to degrade the nylon? I'm for using the correct castle nut and a cotter pin, also, I was trained to fold the short leg down the side of the nut and long leg across the top of the nut. I've never had a cotter pin fail yet when nut is torqued per spec and cotter installed correctly.
Klattu1929,
I never went through any formal mechanical training, but I'm glad to know that at least I've been installing cotter pins right all this time!
alexiskai
Well-known member
It depends on the type of nyloc nut being used, but temp limits of 250° or 350° are common, which would make them suitable for use in a crankcase where they're cooled by oil.
Castellated nuts are common in the aircraft industry because they work well against vibration. The issue with connecting rod nuts is not vibration, the issue is that the rod is being slammed against the nut with explosive force 40 times a second. If the preload is not exactly right, if the rod is able to move at all, it will eventually cut through the cotter pin. And castellated nuts, by their nature, are not suited to precise preloads, because you have to line two of six slots up with the hole in the stud.
Connecting rod failures are a common cause of destroyed Model A blocks, and usually when a postmortem is done, the connecting rod nut is found to have worked its way loose. You can always say "well, if it came loose, it must not have been installed correctly," but this is unfalsifiable. The bottom line is they do come loose, whether through builder error or intrinsic design flaws. So it's unclear to me why you wouldn't want to target this common failure point for improvement.
Synchro909
Well-known member
Only one out of four of my Model A engines has split pins, the rest have either Nylocs or some other self locking nuts. I'll leave it at that.
J Franklin
Well-known member
I used locking nuts on my engine. I got them from McDonald Aiircraft at their surplus store. They were made all metal.
As I recall when I built my '50 Mercury flathead, the 8BA engines used a special self locking, slotted nut and secured them with a pal nut on all the rod caps. No cotter pins were used. Am I remembering this correctly? I would think this type of setup would work well for Model A engines too. Thoughts yea or nay??